Gramineous plants are agriculturally very important plants, including rice, wheat, barley, oat, rye, proso millet, foxtail millet, Japanese millet, corn, finger millet, sorghum, and the like. Gramineous plants having long culms tend to be lodged by strong wind such as typhoon, and thereby the crop yields are serious decreased.
In development of varieties having loading resistance, by seeking a short culm gene, breeding of gramineous plants having short culms has been carried out for many years. However, when the height of a plant is shortened, the panicles and grains of the plant often become reduced in size. Such a short culm gene is not desired from the viewpoint of productivity. Therefore, there is a need for a short culm gene that does not affect panicles and grains, but suitably shortens only plant height.
Among the short culm genes that have ever been found, only sd1 has been put to practical use. The sd1 gene results in a character called “semidwarf”, in which the length of panicles is normal and the height of a whole plant is short. The sd1 gene is a defective form of a C20-oxidase gene for gibberellin (GA) biosynthesis. Varieties of short-culmed rice that are currently cultivated in many areas of the world include Calrose 76 developed in U.S.A., IR 36 developed in south-eastern Asia, Hikari-Shinseiki developed in Japan, and the like. Genetic analyses of these short culm varieties showed that all of the varieties have the same locus as that of the semidwarfing gene sd1. In other words, cultivation of the current short-culmed gramineous plants is governed by only one specific gene, and the only one specific gene is widely used. Considering the purpose of breeding to maintain and expand the genetic diversity of varieties, use of short culm genes other than gene sd1 in breeding to develop varieties having lodging resistance should be encouraged, and new short culm genes are needed.
Recently, a semidwarfing gene, d60 has been newly found (Non-patent literatures 1 and 2). The d60 gene is a gene for shortening the height of a plant by about 20 cm as compared with the height of a plant that does not have the d60 gene.
Coexistence of the semidwarfing gene d60 with gal, which is a gametic lethal gene and universally present in rice, is fatal to both male and female gametes. Therefore, F1 cross (D60d60Galgal) between Koshihikari d60 line, or a variety or line having d60 such as Hokuriku 100 (genotype: d60d60GalGal) and another variety or line (D60D60galgal) shows pollen and seed fertility of 75%, and F2 progeny shows a specific hereditary mode in which it segregates at the ratio of six fertile long-culmed plants (4 D60D60:2 D60d60GalGal):two partial sterile long-culmed plants (D60d60Galgal=F1 type):one short-culmed plant (d60d60GalGal). Thus, Gal is essential to the heredity of d60. The d60 gene is a valuable short culm gene, which would not be obtained in nature without simultaneous artificial mutation of Gal.
The semidwarfing gene d60 has been found to be located on the second chromosome of rice plants and shown to be a gene independent genetically and functionally from sd1 which is located on the first chromosome (Patent Literature 1). A method of selecting gramineous plants having gene d60 and gene Gal has also been developed, in which the method comprises that the presence of gene d60 on the second chromosome and/or the presence of gene Gal on the fifth chromosome which is essential to the heredity of gene d60 are determined using DNA markers or gene markers (Patent Literature 1).
However, the d60 gene has never been identified and the shortening function of d60 has never been elucidated. The d60 gene has never been put to practical use.